Women who are obese are at increased risk of developing psoriatic arthritis whether or not they already have psoriasis, a large, prospective study indicated.

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This prospective study aimed to evaluate the association between obesity and the risk of incident psoriatic arthritis in a large cohort of women.

Note that the study indicates that women who are obese are at increased risk of developing psoriatic arthritis whether or not they already have psoriasis.

Women who are obese are at increased risk of developing psoriatic arthritis whether or not they already have psoriasis, a large, prospective study indicated.

Compared with women whose body mass index (BMI) is below 25, relative risks for psoriatic arthritis were 1.83 (95% CI 1.15 to 2.89) for those with a BMI tween 25 and 30 and 3.12 (95% CI 1.90 to 5.11) for BMI between 30 and 35, according to Abrar A. Qureshi, MD, and colleagues from Harvard.

Moreover, for those whose BMI was above 35, the relative risk was 6.46 times higher (95% CI 4.11 to 10.16, P<0.0001 for trend), they reported in the August issue of Annals of the Rheumatic Diseases.

Although studies have previously linked obesity with both psoriasis and osteoarthritis, little is known about the effects of excess weight on the development of psoriatic arthritis, a condition in which the skin disorder is accompanied by joint damage as well as by systemic abnormalities such as the metabolic syndrome and diabetes.

To investigate a possible connection between obesity and psoriatic arthritis, Qureshi's group analyzed data from the ongoing Nurses' Health Study.

At baseline, participants' mean age was 36, slightly more than 10% were smokers, and mean daily alcohol intake was 3 grams.

Along with current BMI, major weight gain after age 18 also was associated with increased relative risk for psoriatic arthritis among women whether or not they had the skin condition (P<0.0001 for trend):

20 to 50 lbs, RR 1.72 (95% CI 1.09 to 2.72)

50 to 100 lbs, RR 3.67 (95% CI 2.31 to 5.84)

More than 100s lb, RR 7 (95% CI 3.78 to 12.96)

When the analysis was restricted to patients developing psoriatic arthritis after previously having a confirmed diagnosis of psoriasis, the association with increased BMI persisted:

BMI 25 to 30, RR 1.81 (95% CI 1.12 to 2.93)

30 to 35, RR 1.90 (95% CI 1.13 to 3.18)

Above 35, RR 2.98 (95% CI 1.86 to 4.78)

Central obesity also was a risk factor, as participants in the highest tertile of waist circumference were 4.32 times (95% CI 2.27 to 8.24) more likely to develop psoriatic arthritis (P<0.0001).

Secondary analyses found no differences after adjustment for physical activity, smoking, depression, or use of hormone replacement therapy.

The researchers suggested that the association of obesity and psoriatic arthritis may be mediated through systemic inflammation.

"Adiposity can augment cytokine expression by the recruited inflammatory infiltrate, such as interleukin 6 and tumor necrosis factor alpha, relevant to psoriasis pathophysiology," the researchers explained.

In an editorial accompanying the study, Juan D. CaÃ±ete, MD, PhD, of Hospital Clinic in Barcelona and Philip Mease, MD, of Swedish Medical Center in Seattle, further characterized the link between inflammation and obesity as being "bidirectional," with comorbidities further fueling the inflammatory state.

"The 'obesity of psoriasis' is thought to be a key link to the increased risk of diabetes, metabolic syndrome, and cardiovascular disease, but the proinflammatory molecules produced in these conditions also increase susceptibility to psoriasis and the severity of established psoriasis," CaÃ±ete and Mease wrote.

Qureshi and colleagues cautioned that a causal link between adiposity and psoriatic arthritis has yet to be confirmed, and noted that their study may have been influenced by recall, information, or misclassification bias.

"Further studies are warranted to elucidate the underlying mechanisms and clarify the causative association," they concluded.

The study was supported by Brigham and Women's Hospital in Boston.

Qureshi has received grants from Amgen and Pfizer and is a consultant for Abbott, Centocor, Novartis, and the CDC.

Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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